Method and apparatus for ultra thin wafer backside processing

ABSTRACT

A method and apparatus for ultra thin wafer backside processing are disclosed. The apparatus includes an outer ring holding a high temperature grinding and/or dicing tape to form a support structure. An ultra thin wafer or diced wafer is adhered to the tape within the ring for wafer backside processing. The wafer backside processing includes ion implantation, annealing, etching, sputtering and evaporation while the wafer is in the support structure. Alternative uses of the support structure are also disclosed including the fabrication of dies having metalized side walls.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wafer processing and more particularlyto a method and apparatus for ultra thin wafer backside processing.

2. Description of Related Art

Several factors are driving the trend toward thinner chips havingdimensions of less than 4 mils. Such ultra thin chips generally resultin lower substrate resistance, allow for the stacking of chips to meetpackage thickness requirements, and avoid costly thick epitaxial layersin high voltage applications.

Conventionally, a temporary support substrate or carrier can be adhered,usually through an adhesive layer, to the front side of a device waferto facilitate wafer back grinding and a subsequent thin wafer handlingand back side processing. The carrier can be dummy silicon wafer, glasswafer, polymer or polymer based composite substrate, or thick tape. Arigid carrier helps to reduce wafer warping and prevents wafer breakageduring handling and processing. However, removal of the carrier usuallyinvolves complex operations and thus leads to low throughput as well asthe risk of wafer breakage.

In another approach, a rigid edge ring can be formed on the periphery ofa thin wafer to facilitate thin wafer handling and processing. The ringcan be obtained by etching or mechanically back grinding a wafer whileleaving an edge on the wafer periphery intact, or by adhering an extraring on the periphery of a thin wafer. However, this approach suffersthe disadvantage of having a low throughput during wafer thinning and/oredge ring removal, as well as having a reduced active area (due to thewafer area devoted to the circumference).

There is therefore a need in the art for a method and apparatus forultra thin wafer backside processing that overcomes the disadvantages ofthe prior art. The method and apparatus preferably provide for improvedthroughput with low risk of wafer breakage. The method and apparatusalso preferably provide for wafers of 4 to 2 mils thickness and less ata low cost. The method and apparatus further preferably provide for ahigh wafer area usage.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method for ultra thinwafer backside processing includes the steps of mounting a ring and awafer to a high temperature grinding and dicing tape with a wafer frontside adhered to the tape, grinding a wafer back side, wafer back sideprocessing such as ion implantation, annealing, etching andmetallization, followed by wafer dicing.

In accordance with another aspect of the invention, a support structurefor wafer backside processing includes a ring and a tape held by thering, and a wafer adhere able to the tape within the ring.

In accordance with yet another aspect of the invention, a method forultra thin wafer backside processing includes the steps of half dicing awafer, transferring the half diced wafer to a tape supported by a ring,backside grinding the wafer to separate dies, followed by back sideprocessing such as ion implantation, annealing, etching andmetallization.

In accordance with another aspect of the invention, a method ofdepositing metal on side walls of a die includes the steps of forming ormounting a plurality of dies to a tape supported by a ring, anddepositing metal onto a back side and side walls of the plurality ofdie.

There has been outlined, rather broadly, the more important features ofthe invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended herein.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of functional components andto the arrangements of these components set forth in the followingdescription or illustrated in the drawings. The invention is capable ofother embodiments and of being practiced and carried out in variousways. Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other methods and systems for carrying out theseveral purposes of the present invention. It is important, therefore,that the claims be regarded as including such equivalent constructionsinsofar as they do not depart from the spirit and scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 is a top plan view of an apparatus for ultra thin wafer backsideprocessing in accordance with the invention;

FIG. 2 is a side elevation view of the apparatus of FIG. 1;

FIG. 3 is a flow chart of a method for ultra thin wafer backsideprocessing in accordance with the invention;

FIG. 4 is a flow chart of an alternative method of ultra thin waferbackside processing in accordance with the invention;

FIG. 5 is a schematic representation of a die having metalized backsideand side walls mounted to a tape in accordance with the invention;

FIG. 6 is a schematic representation of a die having metalized backsideand side walls in accordance with the invention;

FIG. 7 is a schematic representation of a form having the apparatus ofFIG. 1 mounted thereon;

FIG. 8 is a schematic representation showing the die of FIG. 6 flip chipmounted to a printed circuit board in accordance with the invention; and

FIG. 9 is a schematic representation showing the die of FIG. 6 mountedto a printed circuit board in accordance with the invention and aftersolder reflow.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will now be described in detail with reference tothe drawings, which are provided as illustrative examples of theinvention so as to enable those skilled in the art to practice theinvention. Notably, the figures and examples below are not meant tolimit the scope of the present invention. Where certain elements of thepresent invention can be partially or fully implemented using knowncomponents, only those portions of such known components that arenecessary for an understanding of the present invention will bedescribed, and detailed descriptions of other portions of such knowncomponents will be omitted so as not to obscure the invention. Further,the present invention encompasses present and future known equivalentsto the components referred to herein by way of illustration.

An apparatus for ultra thin wafer backside processing generallydesignated 100 is shown in FIG. 1 and FIG. 2. The apparatus 100comprises an outer ring 110 of generally toroidal configuration that isformed of any rigid material such as metal or a semiconductor. Outerring 110 may have any configuration and preferably has a rectangularcross section for facilitating the use of the apparatus with a clamp.The outer ring 110 may be sized to accommodate therewithin a wafer 140.In an exemplary embodiment, the outer ring 110 may have an outerdiameter of 8 inches to accommodate therewithin a 6-inch wafer.

The apparatus for ultra thin wafer backside processing 100 furthercomprises a high temperature grinding and/or dicing tape 120 affixed orotherwise adhered about the outer ring 110 on a bottom surface 130thereof. The outer ring 110 is operable to provide a holding mechanismfor, and rigid support to, the high temperature tape 120. For thispurpose, the outer ring 110 may also be formed in, and integrated with,other structures. Tape 120 may include a back grinding and/or dicingtape that can resist the temperatures associated with wafer backsideprocessing such as metallization. In combination, the apparatus 100comprising the outer ring 110 and the tape 120 provide a novel supportstructure for wafer backside processing.

The apparatus 100 may be constructed in a step 310 of a method 300 inaccordance with a preferred embodiment of the invention (FIG. 3). Theouter ring 100 and the wafer 140 are mounted to the tape 120 in thisstep. In a step 320 a backside 145 of the wafer 140 is ground andoptionally polished to a desired thickness. Wafers having a thickness onthe order of less than 4 mils are achieved by the method 300.

With the ground wafer supported by the apparatus 100, wafer backsideprocesses such as ion implantation, etching, sputtering, and evaporationare next performed in a step 330. The tape 120 may optionally beannealed to minimize the chance of out-gassing from the tape 120 andit's adhesive. The annealing may be performed in a vacuum furnace.

In a step 340, the wafer 140 is diced from the backside 145 to yield aplurality of die that are then picked in a die pick-up process in a step350. Since direct handling of the ultra thin wafer is reduced to aminimum, a high throughput with low wafer breakage rate is achieved inaccordance with the method of the invention.

In another preferred embodiment of the invention, the wafer 140 may bepartially ground on a separate tape and transferred to the apparatus 100for further processing including further grinding, backside processingand dicing.

In another preferred embodiment of the invention, the wafer 140 may beground to a desired thickness on a separate tape and transferred to theapparatus 100 for further processing including backside processing anddicing.

In yet another preferred embodiment of the invention, the processedwafer may be transferred to another dicing tape, device side face up fordicing and pick up after step 340.

In another preferred embodiment of the invention, the diced wafer (ordies) may be transferred to another tape with device side facing upfollowing step 340 to facilitate pick up in a conventional manner.

In accordance with another embodiment of the invention, the apparatus100 may be employed in a method 400 (FIG. 4). The wafer 140 is halfdiced in a step 410 in a conventional manner. In a step 420, the halfdiced wafer and an outer ring 110 are mounted to a high temperaturegrinding tape 120. The wafer backside 145 is then ground to separate aplurality of dies in a step 430. In a step 440, backside processes suchas ion implantation, native oxide etching, sputtering, and evaporationare performed. The dies are picked up in a step 450. Method 400 iseffective in producing dies down to 1 mil thickness with back metal.

In another preferred embodiment of the invention, the die may betransferred to another tape for pick up after step 440.

In yet another preferred embodiment of the invention, another tape maybe used to complete the dicing before grinding step. The dies may thenbe transferred to the tape 120 and mounted to the outer ring 110 beforestep 440.

In accordance with yet another embodiment of the invention, theapparatus 100 may be employed to deposit metal on die side walls. Thetape 120 having a plurality of die attached thereto can be stretchedwhile being mounted to the outer ring 110 to provide increased spacingbetween the plurality of die. Metal 520 is then deposited on diebacksides 505 as well as side walls 510 of a die 500 as shown in FIG. 5.A completed die 600 having metal 520 on the backside 505 and side walls510 and contact pads 610 on a die front side 620 is shown in FIG. 6.

With reference to FIG. 7, the apparatus 100 is shown clamped to astructure 700 having a curved surface 710. The structure 700 may beformed of metal and the apparatus 100 may be clamped using clamps 720.The curved surface 710 is operable to spread the plurality of die 730adhered to the tape 120. Metal deposition is then used to deposit metalto the die backsides and side walls.

A flip chip 800 having solderable metal on backside 505 and side walls510 is shown mounted to a printed circuit board 900 having a solderpreform 810 formed thereon in FIG. 8.

After solder reflow, contact pads 610 on die 800 make electrical contactwith their corresponding pads on the printed circuit board 900, and backmetal 820 makes electrical contact with contacts 825 and 830 on theprinted circuit board 900, as shown in FIG. 9. A portion of soldermaterial 910 may climb up along the solderable metal surface on die sidewalls and enable solid electrical connection to the die back side.

The inventive methods and apparatus for ultra thin wafer backsideprocessing described herein provide for backside wafer processing thatyields high wafer throughput with low risk of wafer breakage as comparedto other prior art methods. In addition, the methods and apparatus areachievable at a low machine and consumables cost. Wafer area usage ishigh as the supporting frame is provided apart from the wafer itself.

It is apparent that the above embodiments may be altered in many wayswithout departing from the scope of the invention. Further, variousaspects of a particular embodiment may contain patentably subject matterwithout regard to other aspects of the same embodiment. Still further,various aspects of different embodiments can be combined together.Accordingly, the scope of the invention should be determined by thefollowing claims and their legal equivalents.

1. A method for ultra thin wafer backside processing comprising thesteps of: mounting a ring and a wafer to a tape with a wafer front sideadhered to the tape, the wafer mounted within the ring; grinding a waferback side; processing the wafer back side while the wafer is supportedby a support structure formed by the tape and ring; and dicing the waferafter the processing step.
 2. The method of claim 1, wherein the waferback side processing includes a process selected from the groupconsisting of: ion implantation, annealing, etching, sputtering, andevaporation.
 3. The method of claim 1, further comprising annealing thetape before the wafer back side processing step in a vacuum chamber. 4.The method of claim 1, further comprising picking up dies following thedicing step.
 5. The method of claim 1, further comprising transferringthe diced wafer onto another tape and picking up dies with the deviceside facing up.
 6. The method of claim 1, further comprising partiallygrinding the wafer on a separate tape before the mounting step.
 7. Themethod of claim 1, wherein the ring comprises a toroidal ring.
 8. Amethod for ultra thin wafer backside processing comprising the steps of:grinding a backside of a wafer to a desired thickness; mounting thefront side of the ground wafer and a ring to a tape after the grindingstep; processing the wafer back side after the mounting step; and dicingthe wafer after the processing step.
 9. The method of claim 8, whereinthe wafer back side processing includes a process selected from thegroup consisting of: ion implantation, annealing, etching, sputtering,and evaporation.
 10. The method of claim 8, further comprising annealingthe tape before the wafer backside processing step in a vacuum chamber.11. The method of claim 8, further comprising picking up dies followingthe dicing step.
 12. The method of claim 8, further comprisingtransferring the diced wafer onto another tape and picking up dies withdevice side facing up after the dicing step.
 13. The method of claim 8,wherein the ring comprises a toroidal ring.
 14. A method for ultra thinwafer backside processing comprising the steps of: mounting a ring and awafer to a tape with a wafer front side adhered to the tape; grinding awafer back side after the mounting step; processing the wafer back sideafter the grinding step; transferring the processed wafer onto aseparate dicing tape with the wafer back side adhered to the tape; anddicing the wafer.
 15. The method of claim 14, wherein the wafer backside processing includes a process selected from the group consistingof: ion implantation, annealing, etching, sputtering, and evaporation.16. The method of claim 14, further comprising partially grinding thewafer on a separate tape before the mounting step.
 17. The method ofclaim 14, further comprising annealing the tape before the back sideprocessing step in a vacuum chamber.
 18. The method of claim 14, furthercomprising picking up dies following the dicing step.
 19. The method ofclaim 14, wherein the ring comprises a toroidal ring.
 20. A method forultra thin wafer backside processing comprising the steps of: grinding aback side of a wafer to a desired thickness; mounting a front side ofthe ground wafer and a ring to a tape after the grinding step;processing the wafer back side after the mounting step; transferring theprocessed wafer onto a separate dicing tape with the wafer back sideadhered to the tape after the processing step; and dicing the wafer. 21.The method of claim 20, wherein the wafer back side processing includesa process selected from the group consisting of: ion implantation,annealing, etching, sputtering, and evaporation.
 22. The method of claim20, further comprising annealing the tape before the wafer back sideprocessing in a vacuum chamber.
 23. The method of claim 20, furthercomprising picking up dies following the dicing step.
 24. The method ofclaim 20, wherein the ring comprises a toroidal ring.
 25. A supportstructure for thin wafer backside processing comprising: a ring; a tapeaffixed to the ring; and a wafer or a plurality of die being adhere ableto the tape within the ring.
 26. The support structure of claim 25,wherein the ring is toroidal.
 27. The support structure of claim 26,wherein the ring comprises a rectangular cross section.
 28. The supportstructure of claim 25, wherein the tape is made of material that canresist the temperatures of wafer back side processing.
 29. The supportstructure of claim 25, wherein the tape comprises a grinding tape. 30.The support structure of claim 25, wherein the tape comprises dicingtape.
 31. A method for ultra thin wafer backside processing comprisingthe steps of: half dicing a wafer; transferring the half diced wafer toa support structure comprising a ring and a tape; grinding a wafer backside to separate dies; and processing the back sides of the dies. 32.The method of claim 31, further comprising picking up the dies followingthe wafer back side processing.
 33. The method of claim 31, furthercomprising transferring the processed dies onto a separate tape with thedevice side facing up and picking up the dies.
 34. The method of claim31, wherein the wafer back side processing includes a process selectedfrom the group consisting of: ion implantation, annealing, etching,sputtering, and evaporation.
 35. A method for ultra thin wafer backsideprocessing comprising the steps of: half dicing a wafer; back grindingthe wafer to separate dies; transferring the plurality of dies onto asupport structure comprising a ring and a tape; and processing die backsides.
 36. The method of claim 35, further comprising picking up thedies following the wafer back side processing.
 37. The method of claim35, further comprising transferring the processed dies onto a separatetape with the device side facing up and picking up the dies.
 38. Themethod of claim 35, wherein the wafer back side processing includes aprocess selected from the group consisting of: ion implantation,annealing, etching, sputtering, and evaporation.
 39. A method ofdepositing metal on side walls of a die comprising the steps of:mounting a plurality of die on a support structure comprising a ring anda tape; and depositing metal onto a back side and side walls of theplurality of die.
 40. The method of claim 39, wherein the plurality ofdies are formed using a dicing before grinding method on the supportstructure.
 41. The method of claim 39, wherein the plurality of dies areformed using a dicing before grinding method on the tape, the tape beingthen mounted to the ring to form the support structure.
 42. The methodof claim 39, wherein the plurality of dies are mounted onto the tape andthe tape is mounted onto the ring to form support structure after waferseparation into dies on a separate tape.
 43. The method of claim 39,further comprising stretching the tape with dies attached before themounting step onto the ring.
 44. The method of claim 39, furthercomprising clamping the tape to a structure having a curved surfaceduring the deposition step.
 45. The method of claim 44, wherein the tapeis clamped such that the plurality of die are disposed on a convexsurface of the structure.
 46. A die with metal on a back side and sidewalls formed by the method of claim 39.